Heterocyclic compounds such as pyridine currently are recovered as constituents of coal tar, or are synthesized for example by the reaction of acetaldehyde with ammonia and formaldehyde to provide a pyridine, alpha-picoline and beta-picoline product mixture. Specialty heterocyclic aromatic chemicals are utilized in the production of adhesives, pesticides, vitamins, and the like. Another prospective route to heterocyclic aromatic compounds is by the reaction of ammonia or a primary amine with a 2-hydroxymuconic semialdehyde to form a picolinic acid: ##STR1## Subsequent decarboxylation of the picolinic acid could provide the corresponding pyridines and substituted pyridines, as illustrated in the Journal of Organic Chemistry, 37(24), 3938(1972) article by R. J. Moser et al.
A potentially convenient source of 2-hydroxymuconic semialdehyde is by the microbiological oxidation of various hydrocarbon substrates. Microbiological oxidation of aromatic substrates is reviewed by S. Dagley in Advances in Microbial Physiology, 6, 1-47(1971); by P. Chapman in Degradation Of Synthetic Organic Molecules In The Biosphere", pages 17-55, National Academy Of Sciences, 1972; and by P. Williams in "Microbial Degradation Of Xenobiotics And Recalcitrant Compounds", pages 97-107, Academic Press, 1981. Strains of microorganisms are known which metabolize aromatic hydrocarbon substrates by the meta pathway via catechol and 2-hydroxymuconic semialdehyde to biomass and carbon dioxide.
The Nature, 188, 560(1960) article by S. Dagley et al describes the cleavage of catechol by a solution of an enzyme, catechol 2,3-oxygenase, to produce a product with a yellow color in the bioconversion medium. The ultraviolet absorption spectrum indicates a 2-hydroxymuconic semialdehyde type product, which on standing with ammonium hydroxide forms alpha-picolinic acid.
The Canadian Journal of Microbiology, 14 1005(1968) article by R. S. Davis et al describes the metabolism of p-xylene and m-xylene by species of Pseudomonas. A metabolite is produced by a solution of enzyme which has an ultraviolet spectrum consistent with a 2-hydroxymuconic semialdehyde structure. A solution of this metabolite treated with ammonium hydroxide yields a picolinic acid type product.
The Biochemical Journal, 106, 859(1968) publication by R. B. Cain et al also describes the formation of 5-methylpicolinic acid from 4-methylcatechol via 2-hydroxy-5-methylmuconic semialdehyde, utilizing a cell extract prepared from a microorganism grown on toluene sulfonate.
The Journal of Bacteriology, 120(1), 31(1974) publication by G. J. Wigmore et al describes Pseudomonas putida mutants which metabolize phenol and cresols by the meta pathway via catechol and 2-hydroxymuconic semialdehyde intermediates. One mutant strain is described as being defective in both 2-hydroxymuconic semialdehyde hydrolase and dehydrogenase.
The potential of microbiological oxidation of an aromatic substrate such as toluene as a convenient source of 2-hydroxymuconic semialdehyde requires the construction of mutant strains of microorganisms which (1) metabolize an aromatic substrate via catechol or substituted catechol by means of the meta (catechol 2,3-oxygenase) pathway, and (2) allow the accumulation of a 2-hydroxymuconic semialdehyde type metabolite without its further assimilation to other metabolites.
Accordingly, it is an object of this invention to provide a process for the bioconversion of an aromatic hydrocarbon by the meta pathway to accumulated 2-hydroxymuconic semialdehyde or substituted 2-hydroxymuconic semialdehyde.
It is another object of this invention to provide a microbial culture which is capable of metabolizing toluene or substituted toluene, a catechol or substituted catechol, to 2-hydroxymuconic semialdehyde or substituted 2-hydroxymuconic semialdehyde metabolite quantitatively, with an accumulation greater than about 0.1 gram of metabolite per liter of bioconversion medium.
It is a further object of this invention to provide a process for the production of a picolinic acid product from an aromatic hydrocarbon via a 2-hydroxymuconic semialdehyde intermediate.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.